Dialkylamino-thioxomethyl-thioalkanesulfonate compositions have been used for many years in methods for the electrodeposition of metal. During the electrodeposition of metal deposits in the absence of organic brightener and leveler additives, metal deposits often form with a crystalline, matte or burned finish, can vary substantially in thickness from place to place on the deposit, can have pinholes, can have poor elongation properties, and can be high in tensile strength. Such a metal plate can be undesirable from an aesthetic point of view, and can be undesirable in many technological end uses. One major end use of the metal deposit is on a copper plated printed circuit board. The copper deposit on a circuit board should be bright, shiny, lustrous, uniform in thickness, have substantial elongation properties, and modest tensile strength. Bright, shiny boards are easily wetted by solder compositions providing for rapid and efficient connection of electrical components to the printed circuit board. Uniform continuous coatings of copper that have acceptable elongation properties and tensile strength can be resistant to the formation of hairline cracks, which can form during the manufacture and use of the electronic device, that can result in the interruption of the electrical current and in the failure of the electronic device to operate.
One known method for the preparation of the dialkylamino-thioxomethyl-thioalkanesulfonate involves the reaction of dialkyl-dithiocarbamyl chloride with an omega mercaptoalkanesulfonate. The desired sulfonic acid composition is generated at low yields in the reaction along with hydrochloric acid and non-electroactive reaction products. In order to improve yields, an organic base has been suggested in the art to reduce the effect of water on the reaction and to scavenge a hydrochloric acid by-product. However, we have found that an organic base, such as pyridine, did not substantially improve yields of the desired sulfonic acid product.
Another known method involves a simultaneous reaction of an amine, carbon disulfide and an alkane sultone in the presence of alkali metal base to form the desired product. Still another reaction sequence involves the reaction of the amine and carbondisulfide in the presence of sodium hydroxide prior to reaction with the sultone to form the desired product. These preparatory schemes can generate inorganic, nonvolatile by-products and impurities. British Pat. No. 764,613 discloses this procedure.
Accordingly, a substantial need exists for a method for the preparation of a dialkylamino-thioxomethyl-thioalkenesulfonate brightener compositions of high purity at high yield substantially free of substantial quantities of inactive or harmful by-products and avoids generating substantial quantities of nonvolatile impurities which can interfere in electroplating.